Thus in a simple and economical manner a continuously operating electrolytic cell for electro-organic processes is obtained which would otherwise have to be prepared for this purpose and would have a very high cost.
Electrochemical processes using sacrificial electrodes have been long known, and some of them are of applicational interest.
Examples in which the cathode or anode material is consumed during the course of the electrolysis include the production of element-organic compounds such as some alkyl selenides or organometallic compounds such as lead alkyls or Ziegler-Natta catalysts, or the synthesis of coordination compounds such as acetylacetonates, squarates or carboxylates.
However the technology of sacrificial electrode cells is not sufficiently advanced to enable them to be used for electro-organic processes. Of the many models described, only that proposed by Messrs. Nalco (U.S.A.) (P. Gallone, Trattato di ingegneria elettrochimica. publ. Tamburini 1973, pp 595-599) has found large-scale application, and is associated ideally with a heat exchanger comprising a tube bundle in which the steel tubes constitute the cathode and contain in their interior, separated by a mesh of inert material, the lead which is consumed by the anodic reaction. A cooling medium circulates on the outside of the tubes. Without examining in detail the other models described in the literature, and which in any case have not found large-scale application, the construction of a cell with sacrificial electrodes presents problems which have not yet been satisfactorily solved.
As the sacrificial electrode material passes into solution during the electrolysis, if the electrode is in the form of a single metal bar there is a progressive retraction of the metal surface, with an increase in the distance between electrodes and a consequent increase in the cell resistance. This drawback could be overcome by using cells of the Lockheed type (J. F. Cooper, Electric and Hybrid Vehicle System Assessment Seminar, Gainesville, Florida, Dec. 1983) in which the anode metal is consumed against a suitably shaped cathode on which the metal anode bar rests by being held by suitable spacers such that the distance between electrodes remains constant. Other models could be obtained from inorganic electrochemistry, such as the electrolytic refining of metals in which the anode metal, generally in the form of scrap, is fed into a basket and is consumed at a distance between electrodes dictated by the geometry of the basket itself, but the transfer of this type of technology to organic electrochemistry appears problematic.
Obviously in those cases in which the distance between electrodes increases, electrolysis is periodically interrupted in order to open the cell and replace the consumed anodes.
With regard to electro-organic processes, the model which continues to be used is in most cases of the filter press type for which a considerable amount of experience has been obtained and which is commercially available in various versions, so as to satisfy fairly diverse operational requirements. There is therefore an immediate applicational interest in devices which would allow already existing cells of the filter press type and their accompanying technology to be conveniently used for such processes without the complicated equipment required for operating the cells (pumps, tanks, pipes, heat exchangers etc.) having to be substantially modified.
The device described in this patent enables any cell of conventional filter press type to be used by converting it into a continuously operating cell with renewable sacrificial electrodes.